The invention relates to a method for producing a shaft, and an apparatus containing such a shaft.
An apparatus was made known in the German utility-model patent GM 297 02 525.2 that is used, for example, to move window panes, sunroofs, or seats. In order to prevent an undesired axial end play of the armature shaft, it is proposed there that a damper rubber be pressed into a recess of the housing on at least one of its faces. The armature shaft presses a stop disk against this damping rubber. By means of the firmly locking into position and the elastic properties of the damping rubber, the armature shaft remains firmly fixed in place despite ageing processes and signs of wear. Additionally, the armature shaft can be installed very easily and cost-effectively together with the damping rubber. However, the elimination of the axial end play of the armature by means of such a damping rubber limits the maximally permissible tolerance in the production of the armature shaft. Narrower tolerances lead to higher production costs, however, which are undesired in a mass production of the armature shaft.
The method according to the invention has the advantage that the favorable offset of end play with the damping rubber can continue to be used even when the shaft is fabricated not very exact to length in production. By introducing an additional working step, the manufacturing-related length of the shaft subject to tolerance can be decoupled from the elimination of the end play of the shaft. This also makes a very cost-effective and simple manufacture of the endless screw on the armature shaft possible. The end play is suppressed even more reliably as compared with earlier means for attaining the object of the invention, because the tolerance stack-ups are markedly lower after the material displacement than before. The useful We of the armature shaft is increased as a result and clicking noises produced when the direction of rotation changes are reliably prevented.
If the material displacement takes place near an end of the shaft, the stability of the shaft across the entire length is largely maintained. Additionally, the material displacement at this point does not take up any additional space. If the material displacement is carried out by means of burnishing, this is a cost-effective, exact and easy-to-use process. Burnishing brings about a continuous elongation of the shaft that can be well-controlled. The burnishing results in an even constriction, which also has a very advantageous effect on the stability of the shaft. It is also possible to achieve the material displacement simply by means of squeezing, however. Such a working step is less expensive than burnishing, but it does not entirely achieve the same dimensional accuracy.
If the length of the shaft is measured during the material displacement, the nominal dimension of the shaft can be achieved rapidly and exactly in one working cycle.
It proves to be particularly favorable when the shaft is installed in the pole well of the electric motor before the material displacement is started. The tolerances that are stacking up are eliminated as a result. Moreover, the armature shaft then lies in xe2x80x9citsxe2x80x9d bearings, so that the dimensional accuracy and the position of the material displacement can be coordinated with the eventual site of application, particularly when burnishing the material displacement.
It is advantageous to measure the length of the part of the installed shaft extending over the pole well, because the shaft can then be produced to the nominal dimension in the installed state. As a result, the tolerance stack-up of the end play can be markedly reduced.
A further alternative is to measure the set value for the end play during material displacement with the shaft in the installed state. This has the advantage that the measured value of greatest interestxe2x80x94the end playxe2x80x94can be measured directly and it can be adjusted exactly to the set value by means of the material displacement. With this method, all manufacturing and fitting tolerances are completely eliminated.
Efficient process engineering is a further advantage of material displacement by means of burnishing. The endless screw of the armature shaft can be produced and the material displacement can be carried out using just one tool. Even if one tool each is used for the burnishing of the endless screw and the burnishing of the material displacement, one complete working step is spared, because the shaft need be chucked only once for this process. This makes rapid and cost-effective production possible.
The apparatus according to the invention having the features of the independent claim 9 has the advantage that a high-quality product with narrow tolerances is created despite initially great production tolerances of the shaft after installation.
The material displacement located at the end of the shaft and the semicircular cross-sectional area of the circumferential groove have an advantageous effect on the preservation of stability of the shaft. It is advantageous that the shaft diameter can be reduced up to one-half of the original value.